Moses und Aron is Arnold Schoenberg's masterpiece. He composed the first two acts in one intense period from 1930 to 1932, pouring all his thoughts on the compositional process of serialism into the music. The opera is as much a testament to the possibilities of serialism as it is a crucible of Schoenberg's philosophy on God – indeed, to Schoenberg the two were intrinsically linked. Such was the importance of the work as personal and public statement that Schoenberg did not allow its performance in what he considered its unfinished state (he never wrote the music for his libretto of Act III).

So what is serialism? Since Schoenberg's time it has gone on to be used in many different ways, but for Schoenberg it was a way of structuring the 12 chromatic notes – a development of the tonal structuring that predominated in Western music before Schoenberg's innovations. Rather than, for example, a major scale, the way the notes are used is determined by a tone row. A tone row is a specific ordering of all 12 notes – for example, the rising chromatic scale is a tone row, albeit not a very interesting one.

The tone row has several permutations that all count as the row, created through techniques that draw on the ingenious devices Bach used in his contrapuntal music. The row can be stated plainly on each of the 12 notes (Prime). The intervals in a row can be turned upside down (Inversion) so that, for example, a major 3rd up becomes a major 3rd down. Finally, all the Prime and Inversions can be stated backwards (retrograde), giving 48 forms of the row in total. The notes do not need to sound individually and can be stated at the same time – but the order of the chords must be derived from one of the forms of the row.

Schoenberg conceived serialism as a natural progression in Western music, the next step on from the theory of Gesamtkunstwerk (complete art work) that Wagner had introduced. Like Wagner, Schoenberg was strongly influenced by the writings of figures such as Goethe and Schopenhauer – for example, Goethe's idea of the Urpflanze (archetypal plant) of which all plants are variations is a very simple model for the tone row. For Schoenberg, serialism was much more than a technique for giving structural unity to a piece (although this was a key concern) – he saw it as a way to use the uniquely expressive qualities of music to reflect the innate nature of the universe.

Unlike Schoenberg's previous serialist opera Von heute auf morgen, which uses two separate (but related) rows, Moses und Aron is derived from a single row. Schoenberg had initially been worried that a single row could not provide enough material for a work as large as an opera, but found that 'the more familiar I became with this [row] the more easily I could draw themes from it'. Indeed, it's astonishing that the rich and hugely imaginative music of Moses und Aron is so rigorously controlled – but look in the score and it's there. While you might not always (or even more than occasionally) recognize the row, there is a palpable sense that all the music is connected to the same idea, which grows more powerful with repeated listening.

Serialism was never a mathematical problem for Schoenberg. He wrote, 'I cannot often enough warn against the overrating of analysis since it invariably leads to what I have always fought against: the knowledge of how something is made; whereas I have always tried to promote the knowledge of what something is.' But of course how Moses und Aron was made makes it what it is: a highly ambitious effort to describe the impossibility of describing the universe, which, astonishingly achieves that ambition.

The music of this self-taught former wunderkind exists in a shadowy world just on the edge of audibility. Against a fabric of silence interspersed with unmusical knocks, scrapings and shivers, lyrical lines emerge warmly, flaring against the darkness. Sciarrino’s incredibly detailed scores notate complex rhythms that draw on birdsong and chaotic natural forms – but he never disrupts the sense of his text, always making innovative use of the Italian operatic voice.

The elliptical narratives of Sciarrino’s stage works are the perfect complement to this aural world of shadows. They’re stark, spare and elusive, dominated by images that gather a surreal and nightmarish significance. Myth has been a frequent inspiration, from his first opera Amore e Psiche, which had its premiere in 1973. In his second opera, Aspern, Sciarrino began weaving together disparate texts – this adaptation of Henry James’s suspenseful novella uses some of Lorenzo da Ponte’s libretto for Le nozze di Figaro. 1980’s Cailles en sarcophage (Entombed Quails) is a meditation on the cult of fame, which draws on a vast array of texts by authors including Marlene Dietrich and Frank Wedekind.

The surrealist poetry of Jules Laforgue provides the inspiration for two acerbic inversions of Western myth, Lohengrin (1982) and Perseo e Andromeda(1991). 1985’s La perfezione di uno spirito sottile (The perfection of a subtle spirit), on the other hand, is a celebration of nature with sparse scoring for flute, soprano and bells providing windows into sounds of the outside world. Sciarrino had explored these bare textures four years earlier in Vanitas, a hauntingly beautiful ‘still life’ on the fallibility of human life, for a tiny ensemble of mezzo-soprano, cello and piano.

Luci mie traditrici (‘My betraying eyes’, translated by the composer as The Killing Flower) alludes both to the exquisitely complex music of Carlo Gesualdo, whose murder of his wife and her lover is partial inspiration for the opera, and the anachronistic music of Gesualdo’s near contemporary Claude Le Jeune.

Increasingly Sciarrino’s operas have explored themes of isolation and loneliness. Infinito nero (Infinite blackness) for mezzo-soprano and eight instruments sets the ravings of 16th-century Catholic mystic Maria Maddalena de’ Pazzi, as transcribed by eight fellow nuns. Da gelo a gelo (From ice to ice) draws from one year of the fictionalized diaries of Izumi Shikibu, an 11th-century Japanese poet who describes her socially transgressive love affairs in the third person. La porta della legge (The gate to the law) adapts Kafka’s nightmarish examination of an individual crushed by bureaucracy, and in Sciarrino’s hands is a furious indictment of Italy’s current cultural policy. Sciarrino’s latest stage work, Superflumina, is an unshrinking examination of a homeless woman ignored by the stream of commuters who step over her.

Sciarrino’s use of text and silence is unique in opera. But it’s also the fragility of his sound world, its claustrophobia, sadness and breathtaking beauty that make him one of the most compelling composers writing today.

The Killing Flower will be staged by Music Theatre Wales on 24 October 2013. Tickets are still available, although some are available only by ringing or visiting the Box Office in person.